Fiber optic load sensing device

ABSTRACT

A transverse load sensitive optical treadle switch. The switch includes a deformable longitudinal housing and a fiber optic assembly positioned within the housing The fiber optic assembly includes an optical fiber having a first end and a second end, the optical fiber being subject to bending upon application of a transverse load to said housing. Means for mounting the optical fiber in the housing so as to permit bending of the fiber in response to application of a transverse load to said housing are provided, the degree of bending sufficient to cause a significant decrease in passage of light through said fiber when said fiber is bent. Means permitting introduction of light into said optical fiber at the first end of the optical fiber and means for permitting the exit of light from the second end are also provided.

FIELD OF THE INVENTION

The present invention relates generally to switches for sensing thepassage of a vehicle over a treadle, and in particular to a noveltreadle switch design utilizing fiber optics as the sensing means.

BACKGROUND OF THE INVENTION

In toll road and other applications where the passage of a vehicle issensed, it is often required to quantify the number of axles associatedwith a vehicle. This is generally accomplished by means of weightsensitive treadles placed across the roadway.

Conventional treadle designs commonly employ a treadle switch unitconsisting of an elastomeric envelope housing an electrical sensingunit. In one common form, the interior of the envelope is provided withspaced contact strips defined by upper and lower interior surfaces whichare normally separated by air recesses running longitudinally. When theweight of a vehicle wheel is upon the treadle, it deforms the envelopeand causes the contacts to engage each other (electrically) to completea circuit. The electrical sensing means for the treadle switch may, tolike effect, consist of a variable resistor which changes its electricalresistance in response to stress caused by deformation or apiezoelectric sensor which provides a voltage in response to stress. Theimportant feature common to these electrical sensing means is that thesensor produces a readily detectible change in the current and/orvoltage in response to weight applied to the unit.

These treadle switch designs all rely upon electrical current flow andare therefore particularly subject to failure due to intrusion ofmoisture, salts and/or other contaminants. Accordingly, the lifetime ofsuch electrically sensing treadle designs is unduly limited. Becausethese treadles are typically in traffic lanes, replacement causesundesirable disruption of traffic in addition to expense.

This invention relates to a completely sealed treadle switch utilizing afiber optic sensor of the intrinsic type. For comparison, with extrinsicfiber optic sensors, light leaves the fiber and is blocked or reflectedbefore going back into the fiber optic system. Thus, extrinsic opticalsensors have the same disadvantages as photo-electric controls in thatthey ar affected by dirt, contamination and mechanical vibration. Bycontrast, with an intrinsic fiber optic sensor, the light is processed(i.e., is detectably altered due to stress) as it passes along thefiber. This can be in the form of phase angle change or speckle patterndetection, or other attenuation.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide atreadle switch design which overcomes the foregoing disadvantages oftreadle designs with electrical sensors or extrinsic optical sensors.

In particular. it is an object of the present invention to provide atreadle switch having a fiber optic sensor which employs light ratherthan electrical current flow for its sensing operation and is thereforeless subject to failure due to presence of moisture, salts and othercontaminants than electrical sensors.

It is a further object of the present invention to provide a treadlewhich is simple, robust. long lived, and has a high inherentreliability.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, atransverse load sensitive optical switch is provided which includes alongitudinal housing having at least one deformable side and a fiberoptic assembly positioned within the housing. The fiber optic assemblyincludes an optical fiber having a first end and a second end, theoptical fiber being subject to bending upon application of a transverseload to said housing.

The fiber optic assembly also includes means for mounting the opticalfiber in the housing so as to permit bending of the fiber in response toapplication of a transverse load to said housing, the degree of bendingbeing sufficient to cause a significant decrease in passage of lightthrough the fiber when the fiber is bent. Mean permitting introductionof light into said optical fiber at the first end of the optical fiberand means for permitting the exit of light from the second end are alsoprovided.

In a preferred aspect of this embodiment, the means for mounting theoptical fiber include a plurality of fulcrum means positioned along thelength of the optical fiber at intervals sufficient to permit sufficientbending of the optical fiber between the fulcrums in response to atransverse load applied to the housing to substantially alter the amountof light transmitted through the optical fiber.

In another preferred embodiment of the present invention, the transverseload sensitive optical switch comprises a longitudinal housing having atleast one deformable side and a fiber optic assembly positioned withinthe housing. The fiber optic assembly includes a graded optical fiberhaving a first end and a second end longitudinally positioned in saidhousing so as to be subject to bending upon application of a transverseload to the housing, the fiber having an inner core of a material havinga first refractive index and an outer layer of a material having asecond refractive index which is lower than the first refractive index.Means for mounting the optical fiber in the housing adapted to permitbending of the fiber in response to application of a transverse load tothe housing, the degree of bending being sufficient to cause asignificant increase in passage of light from said core to said sleevewhile said fiber is bent, are also provided. Means permitting theintroduction of light into the optical fiber at the first end of theoptical fiber and for permitting the exit of light from the second endare also provided.

In accordance with a further aspect of this embodiment, the means formounting the optical fiber preferably comprises a spiral fiber woundaround the optical fiber, the spiral fiber having adjacent winds spacedapart from one another a predetermined distance averaging at least inthe range of twice the diameter of the optical fiber so as to permitsufficient bending of the optical fiber between the winds of the spiralfiber in response to a transverse load applied to the housing tosubstantially alter the amount of light transmitted through the opticalfiber. The turn of the wound fiber functions essentially as fulcrums tofacilitate bending of the optical fiber.

Advantageously, the switch assembly further comprises a sleevesurrounding the optical fiber and the spiral fiber to keep said spiralfiber wound around said optical fiber and to permit the sufficientbending of the optical fiber. Preferably, the sleeve is made of amaterial which is deformable but relatively stiffer than at least onedeformable side of the housing to facilitate bending of the opticalfiber between the winds of the spiral fiber when a transverse load isapplied to the housing.

In a yet further embodiment of the present invention, a treadle switchunit for vehicular traffic adapted to be mounted transversely on aroadway is provided which comprises a longitudinal elastomeric envelope;a portion of foam rubber embedded within the envelope; and a fiber opticcable supported by the foam rubber within the elastomeric envelope andrunning substantially the length of the treadle switch unit. The fiberoptic cable has a first end adapted to be connected to a signal sourceof light and a second end adapted to be connected a receiving unit,further including means permitting deformation of said fiber optic cablewithin the envelope when a transverse load is applied to the envelopesufficient to significantly alter the amount of light transmittedthrough the fiber optic cable.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be apparent to those skilled in the art in view of thefollowing description and drawings, wherein:

FIG. 1 is a plan view of a treadle unit employing the fiber optic switchof the present invention, with a section broken away;

FIG. 2 is an elevation view of the treadle unit depicted in FIG. 1. witha section broken away;

FIG. 3 is an end sectional view of an optical fiber having an inner coreof higher refractive index and an outer layer of lower refractive indexemployed in a preferred embodiment of the present invention;

FIG. 4 is a sectional elevation view of the optic cable depicted in FIG.3, in its unstressed state, schematically illustrating light passingthrough the core of the optic cable relatively unimpeded;

FIG. 5 is a perspective view, partially in section, of a portion of afiber optic cable constructed in accordance with a preferred embodimentof the present invention;

FIG. 6 is a sectional elevation view of the optic cable depicted in FIG.3, in its stressed and bent state, schematically illustrating lightexiting from the core of the fiber optic cable into the outer layer;

FIG. 7 is a cross-sectional view of the treadle unit depicted in FIG. 1;

FIG. 8 is an end elevation view depicting the treadle unit depicted inFIG. 1 and FIG. 2. mounted in a support frame including a grouping offour treadle switches;

FIG. 9 is a cross-sectional view of a single treadle unit depicted inFIGS. 7 and 8, shown depressed and distorted under a compressive forcesimilar to that as shown applied in FIG. 8; and

FIG. 10 is a schematic depiction of a light signal source and lightsignal receiving unit adapted for use in conjunction with the presentinvention.

DETAILED DESCRIPTION

Turning now to the drawings in detail, and initially to FIGS. 1 and 2thereof, a treadle switch unit 20 in accordance with a preferredembodiment of the present invention is depicted. This treadle switchdevice is generally designated as designed for vehicular traffic, and isadapted to be mounted transversely on a roadway. As depicted in FIG. 8,this treadle unit can be mounted in a fixed frame and can be usedsingularity or in quantity up to and including (4) four treadle switchunits 36, 38. 40 and 42, or more.

The treadle switch unit of the present invention is shown particularlyin the cross-sectional view thereof of FIG. 7 of the drawings andcomprises an envelope preferably of an elastomeric, such as a rubber orurethane, generally designated as 44. The fiber-optic cable is bonded toa base 46 of a soft foam rubber insert supported by the elastomericenvelope of rubber or urethane, which advantageously serves as adeformable side of the envelope. This inner foam rubber allows thecompression and bending of the fiber optic cable when compressive forceis applied as shown in FIGS. 8 and 9. The fiber optic cable shown inFIGS. 1 and 2 is an intrinsic fiber optic cable, 48, bonded to a supportbase of foam rubber 46 and connected to the electronic control sendingand receiving unit 50 through optical connectors 52 and 54.

FIGS. 1 and 2 illustrate the treadle 42 in a singular mode and furtherillustrate the construction of a rubber-urethane envelope having aspecifically designed contour as shown in FIGS. 7, 8, and 9. Thiscontour allows for rapid mounting on the treadle frame assembly 34,locked in place by the wedge locking bars, 56, and secure and protectedby the top cover plates 58.

The fiber optic treadle 20 is a pressure sensitive device molded in arubber compound. It is installed in a frame assembly 34 which lays flushwith the road surface and counts the number of axles on each vehicle.The fiber optic portion of the treadle consists of an optical fiber 22having a "glass" core 24 with a high refractive index (bending of waveof light as it passes from one medium into another) and an outer layer26 having a lower refractive index. The fiber also includes a protectivehard acrylic coating 31. Any light which deviates from the center coreis bent back into the center by the lower refractive index of the outerlayer. If the fiber is bent at a point or points along its length, somelight is guided out of the core into the outer layer where it isdispersed. Light passing down the fiber is virtually switched off bypressure applied the spiral 30. An infra red light (led) is used to sendlight into the sensing fiber.

Turning now to FIG. 3, a preferred embodiment of the transverse loadsensitive fiber optic switch of the present invention employing a gradedoptical fiber 22 is depicted. This graded optical fiber consists of aglass core 24 of high refractive index and an outer layer 26 having alower refractive index. Any light which deviates from the center core isbent back into the center by the lower refractive index of the outerlayer. This is shown in FIG. 4. When the fiber is bent, some of thelight 27 will follow a path through the core, or follow other possiblelight paths or modes of transmission 29 as demonstrated in FIG. 6.

To achieve this micro bending over short or long lengths of fiber, aplastic spiral 30 is used. Preferably, the spiral is wound around theoptical fiber with the winding spaced apart a distance averaging atleast in the range of twice the diameter of the optical fiber. Thispermits bending of the optical fiber to a degree sufficient tosignificantly decrease the amount of light transmitted through theoptical fiber core, without damage to the optical fiber. This is thenpreferably covered with a sleeve 28 to hold the assembly together asshown in FIG. 5. The whole assembly is very flexible and can be takenround corners down to 25 mm radius.

If the fiber is bent at certain points along its length, some light isguided out of the core 24 into the outer layer 26 where it is dispersed,as illustrated in FIG. 6. To the naked eye, light passing down the fiberappears virtually switched off by pressure applied to the spiral. Inaddition, the movement required to give this attenuation is only 0.04min. After this movement the fiber can be squeezed a further 0.1 mmbefore it is over-stressed. When operating over the normal attenuationrange, the fiber has been tested to more than 8 million operationswithout any measurable change in the level of attenuation. Lastly, thereis excellent linearity in the relationship of attenuation to appliedforce.

A light signal source and light signal receiving unit 50 with respectivelight supply and light return connections 54 and 52 to the fiber opticcable. Advantageously, an infra-red light emitting diode (LED) is usedto launch light into the sensing fiber. The light intensity is sensed atthe remote end using a photo detector. By comparing the output level ofthe photo detector with a reference, any change in the amount of lightpassing through the detector can be measured. The power supply to theLED is pulsed at 2 kHz for maximum light intensity. The pulse train ismodified so that 1 in 11 is missed. The missed pulse is used to verifythe control circuit integrity passing through the fiber.

The light intensity is sensed using a photo-detector and by comparingthe output level of the photo detector with a reference, any change inthe amount of light passing through the detector can be measured. Thecontacts are set to open when the signal drops below a threshold (actionsimilar to on/off switch).

FIG. 8 depicts and assembly of four treadles constructed in accordancewith the invention, three of which (treadles 36, 40 and 42) are in thefree, or waiting (unstressed) state shown in FIG. 8. These treadlescarry a pulsed signal light beam from the light power supply, 4, throughthe fiber optic cable and back to the receiving connection of the saidlight power supply, 4. Treadle 8 in FIG. 8 illustrates compression forcebending the fiber optic cable. By knowing the output level of theinfra-red light emitting diode (LED) any deviation in signal light willbe measured by the detector. The voltage free contacts are set to openwhen the signal drops below a threshold. This gives a straight on/offsensor. The structure and operation of the treadle switch unit and theimprovement thereof over known treadle switch units is believed to befully apparent from the above detailed description. It will be furtherapparent that changes may be made in the detailed structure of theimproved treadle switch unit of the invention without departing from thespirit of the invention defined in the appended claims.

What is claimed is:
 1. A treadle sensing device for vehicular trafficadapted to be mounted transversely on a roadway and to receive and sensea downward load of the type imparted by a vehicle wheel comprisingalongitudinal elastomeric envelope having spaced apart longitudinal wallsin a lengthwise region of said envelope adapted to receive said load; aportion of foam rubber embedded within said envelope; a fiber opticcable supported by said foam rubber within said region of saidelastomeric envelope and running generally perpendicular to thedirection of the load to be applied substantially the length of saidregion, said fiber optic cable having a first end adapted to beconnected to a signal source of light and a second end adapted to beconnected to a receiver; means permitting deformation of said fiberoptic cable within said envelope when a transverse load of the typeapplied by a vehicle wheel is applied to said envelope sufficient tosignificantly alter the amount of light transmitted through said fiberoptic cable; and means for preventing complete compression of said foamrubber where said fiber optic cable rests against said foam rubberduring application of said load when said device is mounted on aroadway.
 2. A load sensing device adapted to be mounted transversely ona roadway and to receive downwardly applied loads of the type impartedby an automotive vehicle wheel comprisinga longitudinal envelope havingspaced apart peripheral walls defining an interior space therebetween ina region of said envelope adapted to receive said load, said wallsremaining substantially longitudinally parallel to one anothersubstantially throughout the region of said envelope adapted to receivesaid load, at least one of said walls in said region having anelastically deformable portion having a first interior surfacedeflectable into said interior space towards an opposing second interiorsurface of one of said peripheral walls upon the application of saidload to said envelope; a relatively soft compressible elastomeric insertembedded in said interior space of said envelope; a fiber optic cablelongitudinally positioned within said interior space of said envelopeand resting against said insert, said fiber optic cable comprising anoptical fiber having a first end adapted to receive light and a secondend adapted to permit the exit of said light, said fiber optic cablebeing subject to sufficient deformation into said insert upon deflectionof said first interior surface caused by application of said load so asto permit localized bending of said optical fiber sufficient tosubstantially alter the light transmitted through the optical fiber; andmeans for preventing complete compression of said elastomeric insertwhere said fiber optic cable rests against said elastomeric insertduring application of said load when said device is mounted on thesurface of the roadway.
 3. The load sensing device defined in claim 2,wherein said insert is a foam elastomeric.
 4. The load sensing devicedefined in claim 2, wherein said fiber optic cable is bonded to saidinsert.
 5. The load sensing device defined in claim 2, wherein saidoptical fiber has an inner core of a first refractive index and an outerlayer of a second refractive index which is lower than said firstrefractive index, and wherein said tint end adapted to receive light andsaid second end adapted to permit the exit of said light permitsintroduction and exit of light from said core of said optical fiber. 6.The load sensing device defined in claim 5, wherein said fiber opticcable is a self contained sleeved fiber optic cable assembly comprisingasleeve surrounding said optical fiber; fulcrum means between said sleeveand said optical fiber spaced apart along the length of said opticalfiber a predetermined average distance sufficient to facilitate saidsufficient bending of said optical fiber between said fulcrum means inresponse to a load applied to said deflectable wall portion of saidenvelope to substantially alter the light transmitted through theoptical fiber.
 7. The load sensing device defined in claim 6, whereinsaid fulcrum means comprise a spiral fiber wound around said opticalfiber and disposed within said sleeve.
 8. The load sensing devicedefined in claim 7, wherein said spiral fiber is wound with a distancebetween winds in the range of at least twice the diameter of saidoptical fiber.
 9. The load sensing device defined in claim 6, whereinsaid envelope is made of an elastomeric material and said sleeve is madeof a material which is deformable but relatively stiffer than saidelastomeric material of said envelope to facilitate said sufficientbending of said optical fiber between said fulcrum means when a load isapplied to said envelope.
 10. The load sensing device defined in claim2, wherein said substantial alteration of said light passing throughsaid optical fiber is an attenuation which is substantially linear inresponse to the magnitude of the applied load.
 11. The load sensingdevice defined in claim 2, wherein said substantial alteration of saidlight is substantially complete attenuation of the amount of lightpassing through said optical fiber in response to the applied load. 12.The load sensing device defined in claim 2, wherein said interiorsurface of said deflectable wall portion is substantially fiat whenundeformed.
 13. The load sensing device defined in claim 2, wherein saidenvelope is formed of an elastomeric material.
 14. The load sensingdevice defined in claim 2, wherein said fiber optic cable is U-shapedwithin said envelope.
 15. The load sensing device defined in claim 2,wherein said region of said envelope adapted to receive a load includesan upper wall having an exterior side, said exterior side including agenerally central portion adapted to receive the load to be applied sothat the load to be applied will tend to be concentrated in thegenerally central portion of the exterior side of said upper wall. 16.The load sensing device defined in claim 15, wherein said generallycentral portion includes a convex exterior bump.
 17. The load sensingdevice defined in claim 16, wherein said exterior side of said upperwall includes substantially horizontally fiat exterior portions to thesides of said convex exterior bump.
 18. The load sensing device definedin claim 2, wherein said envelope includes exterior retention surfacesadapted to cooperate with and be retained by a frame assembly.
 19. Theload sensing device defined in claim 18, wherein at least one of saidexterior retention surfaces includes an inwardly sloped exterior sidesurface.
 20. The load sensing device defined in claim 2, wherein saidpreventing means comprises a frame assembly, said frame assemblyincluding frame members adjacent said envelope, said frame membershaving a vertical height sufficient to prevent said complete compressionof said elastomeric insert where said fiber optic cable rests againstsaid elastomeric insert during application of said load.
 21. The loadsensing device defined in claim 20, wherein said frame assembly includesa member partially extending over at least a portion of said envelope,said member leaving a sufficient portion of envelope exposed to the loadto be sensed to permit said sufficient bending of said optical fiber..Iadd.
 22. A treadle sensing device for vehicular traffic adapted to bemounted transversely on a roadway and to receive and sense a downwardload of the type imparted by a vehicle wheel comprisinga longitudinalelastomeric envelope having spaced apart longitudinal walls in alengthwise region of said envelope adapted to receive said load; asubstantially deformable inner member embedded within said envelope; afiber optic cable supported by said substantially deformable innermember within said region of said elastomeric envelope and runninggenerally perpendicular to the direction of the load to be appliedsubstantially the length of said region, said fiber optic cable having afirst end adapted to be connected to a signal source of light and asecond end adapted to be connected to a receiver; means permittingdeformation of said fiber optic cable within said envelope when atransverse load of the type applied by a vehicle wheel is applied tosaid envelope sufficient to significantly alter the amount of lighttransmitted through said fiber optic cable; and means for preventingcomplete compression of said substantially deformable inner member wheresaid fiber optic cable rests against said substantially deformable innermember during application of said load when said device is mounted on aroadway. .Iaddend. .Iadd.23. The device defined in claim 22, whereinsaid substantially deformable inner member includes a relativelycompressible portion. .Iaddend. .Iadd.24. The device defined in claim22, wherein said substantially deformable inner member is adapted todeflect downwardly to a substantial degree where it supports said fiberoptic cable in response to application of said applied load. .Iaddend..Iadd.25. The device defined in claim 22, wherein said substantiallydeformable inner member is a portion of air-conditioning elastomericmaterial. .Iaddend. .Iadd.26. The device defined in claim 22, whereinsaid envelope is mounted with respect to said roadway in such a mannerthat said deformation of said envelope during application of said loadis limited to a predetermined amount. .Iaddend. .Iadd.27. The devicedefined in claim 26, wherein said predetermined amount is a deformationto a position substantially flush with an upper surface of said roadwayproximate to said envelope. .Iaddend. .Iadd.28. The device defined inclaim 22, wherein said envelope is mounted with respect to said roadwaysuch that at least most of said envelope lies below an upper surface ofsaid roadway and at least a portion of said envelope is uncovered byroadway material. .Iaddend. .Iadd.29. The device defined in claim 28,wherein a small portion of said envelope protrudes above said surface ofsaid roadway. .Iaddend. .Iadd.30. The device defined in claim 22,wherein said load sensing device is configured as a vehicle axle counterand further comprises: means operatively connected to said optical fiberfor introducing light into said optical fiber; means operativelyconnected to said optical fiber for receiving said light after it hasbeen transmitted through said optical fiber and for sending saiddetectable alteration of said light caused by deformation of saidoptical fiber; means operatively connected to said means for receivingand sensing said light for determining whether a predetermined thresholdvalue of alteration of said light exists; and means operativelyconnected to said threshhold determining means for causing a count whensaid threshhold value of alteration of said light exists due to thepassage of said vehicle wheel over said device. .Iaddend. .Iadd.31. Asensing device for vehicular traffic adapted to be mounted transverselyon a roadway and to receive and sense a downward load of the typeimparted by a vehicle wheel as the wheel passes over the devicecomprisinga longitudinal deformable envelope having a lengthwise regionadapted to receive said load, said envelope being mounted with respectto said roadway at least partially exposed such that application of saidload will cause deformation of said envelope; and a fiber optic cabledisposed within said region of said envelope and running generallyperpendicular to the direction of the load to be applied substantiallythe length of said region, said fiber optic cable including an opticalfiber adapted to be connected to a signal source of light and to areceiver, said fiber optic cable being disposed within said envelopesuch that deformation of said envelope in response to said load willcause deformation of said fiber optic cable and its included opticalfiber sufficient to detectably alter the light transmitted through saidoptical fiber without overstressing said optical fiber upon amultiplicity of repeated applications of said load. .Iaddend. .Iadd.32.A sensing device for vehicular traffic adapted to be mountedtransversely on a roadway and to receive and sense a downward load ofthe type imparted by a vehicle wheel as the wheel passes over the devicecomprising a longitudinal elastomeric envelope having a lengthwiseregion adapted to receive said load, said envelope being adapted to bemounted with respect to said roadway such that application of said loadwill cause deformation of said envelope; and a fiber optic cabledisposed within said region of said elastomeric envelope and runninggenerally perpendicular to the direction of the load to be appliedsubstantially the length of said region, said fiber optic cableincluding an optical fiber adapted to be connected to a signal source oflight and to a receiver, said fiber optic cable being disposed withinsaid envelope such that deformation of said envelope in response to saidload will cause deformation of said fiber optic cable and its includedoptical fiber sufficient to detectably alter the light transmittedthrough said optical fiber, said envelope being mounted with respect tosaid roadway in such a manner that said deformation of said envelopeduring application of said load is limited to a predetermined amount toprevent overstressing said optical fiber upon a multiplicity of repeatedapplications of said load. .Iaddend. .Iadd.33. The device defined inclaim 32, wherein said predetermined amount is a deformation to aposition substantially flush with an upper surface of said roadwayproximate to said envelope. .Iaddend. .Iadd.34. The device defined inclaim 32, wherein said envelope is mounted with respect to said roadwaysuch that at least most of said envelope lies below an upper surface ofsaid roadway and at least a portion of said envelope is uncovered byroadway material. .Iaddend. .Iadd.35. The device defined in claim 34,wherein a small portion of said envelope protrudes above said surface ofsaid roadway. .Iaddend. .Iadd.36. A sensing device for vehicular trafficadapted to be mounted transversely on a roadway and to receive and sensea downward load of the type imparted by a vehicle wheel as the wheelpasses over the device comprising a longitudinal elastomeric envelopehaving at least one deformable side in a lengthwise region of saidenvelope adapted to receive said load and means defining a longitudinalcavity in said lengthwise region, said envelope being adapted to bemounted with respect to said roadway such that application of said loadto cause deformation of said deformable side will cause deformation ofsaid longitudinal cavity; a compressible cushion within said envelope ina portion of said envelope disposed below said longitudinal cavity; afiber optic cable disposed within said means defining a longitudinalcavity in said region of said envelope and running generallyperpendicular to the direction of the load to be applied substantiallythe length of said region, said fiber optic cable including an opticalfiber adapted to be connected to a signal source of light and to areceiver, said fiber optic cable being disposed within said envelopesuch that deformation of said cavity in response to said load will causedeformation of said fiber optic cable and its included optical fibersufficient to detectable alter the light transmitted through saidoptical fiber, said envelope being adapted to be mounted with respect tosaid roadway as to prevent complete compression of said cushion duringapplication of said load. .Iaddend. .Iadd.37. A sensing device forvehicular traffic mounted transversely on a roadway and adapted toreceive and sense a downward load of the type imparted by a vehiclewheel as the wheel passes over the device comprisinga longitudinalenvelope having at least one deformable wall and means defining alongitudinal cavity in a lengthwise region of said envelope adapted toreceive said load, said longitudinal cavity being subject to deformationupon deformation of said deformable wall; a compressible cushiondisposed in said envelope below said longitudinal cavity; a fiber opticcable disposed within said cavity in said region of said elastomericenvelope and running generally perpendicular to the direction of theload to be applied substantially the length of said region, said fiberoptic cable including an optical fiber adapted to be connected to asignal source of light and to a receiver; means permitting deformationof said fiber optic cable and said included optical fiber within saidlongitudinal cavity of said envelope when a transverse load of the typeapplied by a vehicle wheel is applied to said envelope sufficient todetectably alter the light transmitted through said optical fiber. saidenvelope being mounted with respect to said roadway in such a manner asto prevent complete compression of said cushion. .Iaddend. .Iadd.38. Thedevice defined in claim 37, wherein said envelope is formed ofelastomeric material. .Iadd.39. The device defined in claim 37, whereinsaid load sensing device is configured as a vehicle axle counter andfurther comprises: means operatively connected to said optical fiber forintroducing light into said optical fiber; means operatively connectedto said optical fiber for receiving said light after it has beentransmitted through said optical fiber and for sensing said detectablealteration of said light caused by deformation of said optical fiber;means operatively connected to said means for receiving and sensing saidlight for determining whether a predetermined threshhold value ofalteration of said light exists; and means operatively connected to saidthreshhold determining means for causing a count when said threshholdvalue of alteration of said light exists due to the passage of saidvehicle wheel over said device.